The present invention relates to apparatus which emits high-frequency electromagnetic waves, and in particular to an antenna and antenna feed device which allows the energy emitted by the antenna to be accurately adjusted in respect of power and position.
Hereinafter, the energy will in all cases be measured at the point of use. If for example what are involved are medical applications of the apparatus, the energy measured will be that received at the skin of the patient in the area to be treated.
Such devices can be applied in very many fields and in particular in all those where research, development and industry require the application of an electromagnetic field under extremely accurate conditions as regards location and/or power. In prior art devices, when it is desired to produce a strong electromagnetic field over a small area, or a concentrated field, or one which is distributed in a precise pattern, or again when it is desired to shift the field continuously or discreetly, recourse is usually had to very bulky and generally somewhat inaccurate apparatus. However, the bulk considerably restricts possible uses and the general trend towards miniaturisation poses problems which cannot be solved simply by a change of scale. It is clear that there are techniques, such as those used in astronautics, which are relying to a greater and greater extent on equipment which is extremely light and extremely versatile in production and in use. If for example it is desired to produce an electromagnetic field in areas which are difficult of access or on objects which are small in size, the use of conventional antennas soon presents problems.
Furthermore, in accordance with the desiderata upon which the present invention is based, the apparatus should be able to emit purely electrical fields or currents, at the same time as or alternately with trains of electromagnetic waves.
This would enable the electromagnetic fields and the electrical currents to be separated and in particular it enables thermal phenomena, which are often a nuisance, to be controlled, as will be seen below.
Also a further object of the invention is to provide such apparatus particularly suitable for biological applications, and in particular medical or veterinary applications. It should in fact be able to be used "in situ", that is to say in the immediate vicinity of the area to be treated, or possibly in an implanted position.
There are many kinds of apparatus in the prior art for generating electrical currents or for emitting magnetic, electrical or electromagnetic fields which operate in fairly varied frequency bands. Such pieces of apparatus may operate either as current generators or as field emitters and may do so for either temporary or long-term use on the premises of the person giving treatment or by the patient's bed. They may operate continuously or intermittently. Such pieces of apparatus are more bulky or less transportable the higher the level of the energy given out and becuase high voltages are normally used. The therapeutic effects are generally considered to depend on the amount of energy received in the tissues to be treated and on certain other physical, and especially thermal, parameters.
Such pieces of apparatus can only be used where there is a qualified medical staff and if the patient is brought to the place of use, which often involves frequent and painful journeys. Because of this, there are numerous occasions on which people fail to take treatment which could bring about a significant reduction in the healing period, for example in cases of immobilisation in plaster following bone fractures.
To avoid any confusion, the basic vocabulary will be reviewed taking the example of biological and medical applications as a basis. When use is made of current, at least two electrodes are employed, these electrodes being applied to the patient, who becomes a conductive element in the circuit. This chiefly produces various physical and chemical effects (a thermal Joule effect, inophoresis which provides for the passage of ions through the tissues, etc.) and nerve effects (a motor exciting effect). The currents used are often termed galvanic (continuous) or faradic (pulsed). Use has also been made in the prior art, of what have for long been known as short waves. What this involves is creating a capacitive, and thus purely electrical, field by means of at least two plates or electrodes which are placed on either side of the patient, generally at a distance from him or her, the patient becoming a di-electric element. The di-electric losses then give rise to heating. Operations often take place with only one electrode or plate with the patient forming an earth. This may result in a sparking phenomenon between the electrode and the patient. In none of these short wave techniques is there any attempt to achieve a magnetic field effect.
Use has also been made of apparatus for emitting electromagnetic fields, which usually relies on induction coils. However, the present day trend is to use higher and higher energy levels and in particular high voltages, which results in vast pieces of equipment and makes them difficult to use for many applications, as was stated above.